A living biological sample can be observed by an optical microscope as it is. Therefore, the optical microscope is used as a very effective tool in elucidating a life phenomenon. A fluorescent probe having various functions has been developed, and further, cell functions have been elucidated and a single molecule has been observed by utilizing various optical systems such as a phase difference optical system, a confocal optical system, and a full reflection fluorescent observation. There have been many accomplishments and much expertise for a long period of time in observing a living sample by using light.
One of targets of elucidation of the life phenomenon is expected to clarify not the function of one minimum constituent element such as a cell or a protein but the interaction between plural constituent elements, the mechanism of information transmission, the mechanism of energy transmission, the dynamics of an information molecule inside of a cell. The function of an organ of a living body depends on the interaction between cells as the minimum constituent elements of the living body. As a consequence, it is necessary to clarify the interaction between the cells so as to elucidate the detailed mechanism of the organ. In addition, it is necessary to understand the dynamics of plural living molecules by observation at real time.
In the meantime, a spatial resolution by the optical microscope is restricted by properties of an optical wave, and therefore, the resolution can be achieved in only the order of submicron. As a consequence, it is necessary to develop an optical microscope having a higher spatial resolution so as to elucidate the interaction between plural molecules or minute organs and an information transmission mechanism.
A near-field microscope has been known as a microscope for optically observing a minute region in excess of an optical diffraction limit. FIG. 1 is a diagram illustrating the principle of a near-field microscope. As illustrated in FIG. 1, a laser beam is incident into a tip of a probe shielded with metal. An aperture is formed at the tip of the probe in several nm to several tens nm. The aperture is very smaller than an optical wavelength, and therefore, the laser beam incident into the tip of the probe cannot pass through the aperture. However, a part of the laser beam evanesces from the aperture by a so-called near-field effect (i.e., an evanescent wave). The interaction between a near-field light beam evanescing from the tip of the probe and an object to be measured is observed.
The use of the near-field microscope achieves the observation of the minute region smaller than the optical wavelength. However, the tip of the probe need be observed in the proximity of the object to be measured by the near-field microscope. Hence, the object to be measured is observed while it is scanned by the probe, as illustrated in FIG. 2, thereby taking much time in observing a two-dimensional image. Although the observation at real time is needed for observing the dynamics of a living body, the near-field microscope in the prior art cannot achieve the observation at real time.
Japanese Patent Application Laid-open (JP-A) No. 2003-524779 and JP-A No. 2006-308475 are listed as prior art literature relating to the invention. JP-A) No. 2003-524779 discloses a near-field microscope using a near-field light beam, in which a near field is produced with the irradiation of light beams through plural pores at nano scale. Moreover, JP-A) No. 2003-524779 suggests excitation of a light beam with an electron beam.
JP-A No. 2006-308475 discloses a near-field microscope for irradiating a living sample with a light beam, converting a generated near-field light beam into an electron beam by an optoelectronic conversion membrane, and detecting the electron beam.